Regioselective Dearomative Amidoximation of Nonactivated Arenes Enabled by Photohomolytic Cleavage of N-nitrosamides.

Dearomative spirocyclization reactions represent a promising means to convert arenes into three-dimensional architectures; however, controlling the regioselectivity of radical dearomatization with nonactivated arenes to afford the spirocyclizative 1,2-difunctionalization other than its kinetically preferred 1,4-difunctionalization is exceptionally challenging. Here we disclose a novel strategy for dearomative 1,2- or 1,4-amidoximation of (hetero)arenes enabled by direct visible-light-induced homolysis of N-NO bonds of nitrosamides, giving rise to various highly regioselective amidoximated spirocycles that previously have been inaccessible or required elaborate synthetic efforts. The mechanism and origins of the observed regioselectivities were investigated by control experiments and density functional theory calculations.

Spiro-buckybowls: Synthesis and Selective Transformations toward Chiral and Nonlinear Optical Polycycles.

Integration of spirocycles with buckybowls is a promising strategy to construct three-dimensional (3D) curved π-systems and to endow distinctive physicochemical features arising from buckybowls. Herein, a series of carbon-bridged spiro-type heterosumanenes (spiro-HSEs) were synthesized by combining 9,9'-spirobifluorene and dichalcogenasumanenes (DCSs). It is found that spiro-conjugation plays an important role in the geometric and electronic structures of spiro-HSEs. The bowl depth of DCSs moiety becomes larger in the spiro-HSEs. Owing to the Jahn-Teller (J-T) effect, two DCSs segments of spiro-HSEs have different bowl depths accompanied with the unequal distribution of charge in radical cation state. Taking advantage of the typical reactions of DCSs, selective transformations of spiro-HSEs have been adopted in accordance to the nature of chalcogen atoms (S, Se, Te) to bestow the value-added functionalities. The emissive property is enhanced by converting the thiophene rings of S-doped spiro-HSE into thiophene S,S-dioxides. A chiroptical polycycle could be produced by ring-opening of the edge benzene of Se-doped spiro-HSE. The covalent adduct of Te-doped spiro-HSE with Br2 forms non-centrosymmetric halogen-bonded networks, resulting in the high performance second-order nonlinear optics (NLO).

Ultrasensitive and Label-Free Detection of Copper Ions by GHK-Modified Asymmetric Nanochannels.

Artificial solid-state nanochannels have garnered considerable attention as promising nanofluidic tools for ion/molecular detection, DNA sequencing, and biomimicry. Recently, nanofluidic devices have emerged as cost-effective detection tools for heavy metal ions by modifying stimuli-responsive materials. In this work, high-purity glycyl-l-histidyl-l-lysine (GHK) peptide is synthesized by using 7-diphenylphosphonooxycoumarin-4-methanol (DPCM) as a protecting group and auxiliary carrier by homogeneous synthesis of photocleavable groups. Subsequently, we developed a GHK-modified asymmetric nanochannel nanofluidic diode by covalently attaching the GHK peptide to the inner surface of the nanochannels. This modification facilitated specific recognition and ultra-trace level detection of Cu2+ ions, achieving a detection limit of 10-15 M. Due to the robust complexing ability between Cu2+ and GHK peptide, the GHK-modified asymmetric nanochannels can form GHK-Cu complexes on the inner surface of nanochannels when Cu2+ passes through the nanochannels. This results in changes of current-potential (I-V) properties, which facilitated Cu2+ detection. Theoretical calculations confirmed the high affinity of the GHK peptide for Cu2+, thereby ensuring excellent Cu2+ selectivity. To evaluate the applicability of our system for detecting Cu2+ in real-world scenarios, we analyzed the concentration of Cu2+ in tap water. The GHK-Cu complexes could be dissociated by adding EDTA to the solution, enabling the regeneration and reuse of this ultrasensitive and label-free Cu2+ detection system using GHK-modified asymmetric multi-nanochannels. We anticipate that the GHK-modified asymmetric nanochannels will find future applications in the label-free detection of Cu2+ in domestic water.

Bottom-Up Preparation of Twisted Graphene Nanoribbons by Cu-Catalyzed Deoxygenative Coupling.

Graphene nanoribbons (GNRs) are promising in organic optoelectronic materials, and their properties largely depend on the size, edge, and conformation. Herein, the fully armchair-edged GNRs (AGNRs) with lengths up to 2.65 nm by using a Cu-catalyzed deoxygenative coupling as a key step. The resulting AGNRs (2HBT, 3HBT, and 4HBT) possess highly twisted π-scaffolds, and the torsion angles between the adjacent triphenylene moieties are larger than 32°, as proved by crystallographic analyses. Theoretical and spectroscopic studies show that the butoxy groups endow AGNRs with electron-rich features, the extension of the π-system from 2HBT to 4HBT reinforces S0 →S1 excitation, and the distortion of the π-scaffold enhances the fluorescence quantum yield (ΦF ). In particular, 4HBT has the lowest oxidation potential (Eox 1 =0.55 V vs. SCE) and displays red fluorescence with a ΦF value of 81 %.

Lasing from an Organic Micro-Helix.

Organic solid-state semiconductor lasers are attracting ever-increasing interest for their potential application in future photonic circuits. Despite the great progress made in recent years, an organic laser from 3D chiral structures has not been achieved. Now, the first example of an organic nano-laser from the micro-helix structure of an achiral molecule is presented. Highly regular micro-helixes with left/right-handed helicity from a distyrylbenzene derivative (HM-DSB) were fabricated and characterized under microscope spectrometers. These chiral micro-helixes exhibit unique photonic properties, including helicity-dependent circularly polarized luminescence (CPL), periodic optical waveguiding, and length-dependent amplified spontaneous emission (ASE) behavior. The successful observation of laser behavior from the organic micro-helix extends our understanding to morphology chirality of organic photonic materials and provides a new design strategy towards chiral photonic circuits.

Construction of Dopamine-Releasing Gold Surfaces Mimicking Presynaptic Membrane by On-Chip Electrochemistry.

We report a strategy to construct a dopamine-releasing gold surface mimicking a presynaptic membrane on a microfluidic chip to simulate in vivo neural signaling. We constructed dopamine self-assembled monolayers (DA SAMs) by electrochemical deprotection of methyl group-protected DA SAMs on a gold surface. Electrochemically controllable release of DA SAMs can be realized by applying nonhydrolytic negative potential on the gold surface. Our method in constructing DA SAMs avoids the polymerization and protonation of DA molecules which may lead to the failure of the DA SAM formation. By combining microfluidics, we realized spatial and temporal controllable release of DA by electrochemistry from the gold surface. Furthermore, by culturing neurons on the patterned DA SAMs, the interface between the DA SAMs and the neurons could serve as a presynaptic membrane, and the spatiotemporal release of DA could modulate the neuron activity with high precision. Our study holds great promise in the fields of neurobiology research and drug screening.

Dissecting Trichalcogenasumanenes: π-Bowl to Planar, Invertible Curvature, and Chiral Polycycles.

The buckybowl trichalcogenasumanenes show cleavage of flanking benzene ring upon oxidation, which leads their dissection by fusing various amidine moieties onto peripheral region. By gradually increasing the ring size of amidine from five- to six- and seven-membered, the molecule engineering results in the [7-5-6]-, [7-6-6]-, and [7-7-6]-fused polycycles. Three systems are distinct in the molecular geometries, packing motifs, and optoelectronic properties. The [7-5-6]-fused case adopts the flat backbone, displays strong emission with the fluorescence quantum yield up to 52.3 %, and undergoes a two-photon absorption process. The [7-6-6]-fused one is of a curvature with molecular geometry inversion, forms a tight stack of curved π-system, shows broad absorption extended to 700 nm, and exhibits the p-type semiconducting behavior with hole mobility of 4.4×10-3  cm2 V-1 s-1 . The [7-7-6]-fused one possesses the highly twisted skeleton to show stable chirality, and exhibits red emission in both solution and solid state. The surgery on trichalcogenasumanene is a promising approach to create polycycles with diverse functionalities.

4,5,9,10-Pyrene Diimides: A Family of Aromatic Diimides Exhibiting High Electron Mobility and Two-Photon Excited Emission.

The design and synthesis of high-performance n-type organic semiconductors are important for the development of future organic optoelectronics. Facile synthetic routes to reach the K-region of pyrene and produce 4,5,9,10-pyrene diimide (PyDI) derivatives are reported. The PyDI derivatives exhibited efficient electron transport properties, with the highest electron mobility of up to 3.08 cm2 V-1 s-1 . The tert-butyl-substituted compounds (t-PyDI) also showed good one- and two-photon excited fluorescence properties. The PyDI derivatives are a new family of aromatic diimides that may exhibit both high electron mobility and good light-emitting properties, thus making them excellent candidates for future optoelectronics.

Trichalcogenasumanene ortho-Quinones: Synthesis, Properties, and Transformation into Various Heteropolycycles.

The regioselective transformation of heterobuckybowl trichalcogenasumanenes 1 a,b at peripheral butoxy groups afforded trichalcogenasumanene ortho-quinones 2 a,b. Compounds 2 a,b are distinct from 1 a,b in terms of their molecular geometry and electronic state; that is, they have a shallower bowl depth and show absorbance in the NIR region. The reaction of 2 a,b with diamines resulted in a variety of heteropolycycles, including molecular spoon 3 a-6 a, planar π-systems 3 b-6 b, and highly twisted [7-6-6]-fused systems 7 a,b. These new heteropolycycles had different optical/electrical properties: 4 a,b showed hole mobility of approximately 0.002 cm2 V-1 s-1 , 6 a displayed red emission in both solution and the solid state, and 7 a,b formed tight stacks of the curved π-surface.

Accessing the Triplet State in Heavy-Atom-Free Perylene Diimides.

Previous studies of perylenediimides (PDIs) mostly utilized the lowest singlet excited state S1 . Generation of a triplet excited state (T1 ) in PDIs is important for applications ranging from photodynamic therapy to photovoltaics; however, it remains a formidable task. Herein, we developed a heavy-atom-free strategy to prompt the T1 ←S1 intersystem crossing (ISC) by introducing electron-donating aryl (Ar) groups at the head positions of an electron-deficient perylenediimide (PDI) core. We found that the ISC efficiency increases from 8 to 54 % and then to 86 % by increasing the electron-donating ability of head-substituted aryl groups from phenyl (p-PDI) to methoxyphenyl (MeO-PDI) and then to methylthioxyphenyl (MeS-PDI). By enhancing the intramolecular charge-transfer (ICT) interaction from p-PDI to MeO-PDI, and then to MeS-PDI, singlet oxygen generation via energy-transfer reactions from T1 of PDIs to (3)O2 was demonstrated with the highest yield of up to 80 %. These results provide guidelines for developing new triplet-generating PDIs and related rylene diimides for optoelectronic applications.

ortho-Heterofluorene perylenediimides: synthesis, photophysical, and exciton dynamic properties.

Previous studies suggest the perylenediimide (PDI) triplet excited state (T1) have been accessible only through bimolecular sensitization, the internal heavy-atom effect or a sophisticated cascade of nonradiative processes. Here, we designed heavy-atom-free PDIs to prompt the Tn ← S1 intersystem crossing (ISC) by introducing electron donating heterofluorene groups at the head positions of the electron-deficient PDI core. We obtained relatively high ISC efficiency up to 92% yield. Furthermore, promptly generated PDI triplets can sensitize the molecular oxygen quantitatively to yield 1O2, with singlet oxygen generation efficiencies (ΦΔ) near to unity. These results further suggest that the ISC process of PDIs can be enhanced through the intramolecular charge transfer (ICT) interaction, providing guidelines for developing triplet-generating PDIs and related rylene diimides for optoelectronic applications.

Self-Assembled Microdisk Lasers of Perylenediimides.

Organic solid-state lasers (OSSLs) have been a topic of intensive investigations. Perylenediimide (PDI) derivatives are widely used in organic thin-film transistors and solar cells. However, OSSLs based on neat PDIs have not been achieved yet, owing to the formation of H-aggregates and excimer trap-states. Here, we demonstrated the first PDI-based OSSL from whispering-gallery mode (WGM) hexagonal microdisk (hMD) microcavity of N,N'-bis(1-ethylpropyl)-2,5,8,11-tetrakis(p-methyl-phenyl)-perylenediimide (mp-PDI) self-assembled from solution. Single-crystal data reveal that mp-PDI molecules stack into a loosely packed twisted brickstone arrangement, resulting in J-type aggregates that exhibit a solid-state photoluminescence (PL) efficiency φ > 15%. Moreover, we found that exciton-vibration coupling in J-aggregates leads to an exceptional ultrafast radiative decay, which reduces the exciton diffusion length, in turn, suppresses bimolecular exciton annihilation (bmEA) process. These spectral features, plus the optical feedback provided by WGM-hMD microcavity, enable the observation of multimode lasing as evidenced by nonlinear output, spectral narrowing, and temporal coherence of laser emission. With consideration of high carrier-mobility associated with PDIs, hMDs of mp-PDI are attractive candidates on the way to achieve electrically driven OSSL.

An electrochemically switched smart surface for peptide immobilization and conformation control.

We report an electrochemically switched smart surface for controlled peptide immobilization and conformation control. This dynamic surface is based on self-assembled monolayers (SAMs) containing surface-bound trimethoxybenzene moieties, which can undergo electrochemically modulated surface activation to be stepwisely converted to two catechol derivatives. This new smart surface can be used to realize stepwise immobilization of a peptide, and more importantly, to control peptide conformation on a surface. We demonstrate herein that with one electrochemical activation step, a linear peptide containing an RGD sequence can be attached onto the SAMs. With the subsequence activation step, the attached linear RGD peptide can be converted into cyclic conformation. The SAMs bounded with linear and cyclic RGD exhibit different adhesion behaviors to fibroblasts cells. The reaction procedure can be well-monitored by cyclic voltammetry (CV), electrochemical surface enhanced Raman microscopy (EC-SERS), and X-ray photoelectron spectroscopy (XPS). It is believed this robust smart surface can find wide applications in surface immobilization of bioactive moieties.

Layer-by-layer assembly of homopolypeptide polyelectrolytes on asymmetric nanochannels for the detection of nickel ions.

Nickel stands out as one of the prevalent heavy metal ionic pollutants found in water. It is urgent to devise a simple, efficient, budget-friendly, highly-selective and proficient method for detecting Ni(II). This work reports an approach to design a nanofluidic diode for the ultrasensitive and label-free detection of nickel ions based on layer-by-layer assembly of polyarginine (PA) and polyglutamic acid (γ-PGA) on the inner surface of asymmetric nanochannels. We can tune the adsorption/desorption characteristics of the asymmetric nanochannels for Ni2+ by adjusting the pH changes, i.e., the PA-γ-PGA modified nanochannels adsorb Ni2+ at pH 6 and desorb at pH 3 in aqueous solution. This pivotal adjustment facilitates the reusable and specific detection of nickel ions with a detection limit of 1 × 10-8 M. Moreover, the system demonstrates commendable stability and recyclability, enhancing its practical applicability. This innovative system holds promise for recognizing and detecting nickel ions in diverse environments such as water, blood, and cells. The robust performance and adaptability of our proposed system instill confidence in its potential for future applications.

Linear Non-benzenoid Isomer of Acene Fusing Chrysene with Azulene Units.

Non-benzenoid polycyclic aromatic hydrocarbons (PAHs) have received considerable attention owing to their distinctive optical and electrical properties. Nevertheless, the synthesis and optoelectronic application of non-benzenoid PAHs remain challenging. Herein, we present a facile synthesis of linear non-benzenoid PAH with an armchair edge, diACh, by fusing chrysene with two azulene units. We systematically investigated the optical and electrical properties, which were also compared to its isomers, including benzenoid and non-benzenoid zigzag edge isomers. diACh exhibits global aromaticity, good planarity, and suitable highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels. The protonation of diACh in solution successively forms a stable tropylium cation and dication. Moreover, the neutral, cationic, and dicationic states of diACh can be transformed with remarkable reversibility during the protonation-deprotonation process, as confirmed by ultraviolet-visible absorptions, fluorescence spectra, 1H nuclear magnetic resonance, and theoretical calculations. Additionally, we fabricate p-type organic field-effect transistor (OFET) devices based on diACh with hole mobility up to 0.026 cm2 V-1 s-1, and we further develop OFET-based acid vapor sensors with good sensitivity, recyclability, and selectivity. These findings underscore the unique properties of linear non-benzenoid PAHs with an armchair edge engendered by the fusion of azulene with the acene backbone, showcasing prospective applications in organic optoelectronics.

Investigation of an electrochemically switched heterocyclization reaction on gold surface.

We report an investigation of an electrochemically switched heterocyclization reaction on hydroquinone-terminated self-assembled monolayers (SAMs). This reaction involves an electrochemically modulated hydroquinone/benzoquinone transformation step in the SAMs and a subsequent heterocyclization step taking place between the electrochemically generated benzoquinone moieties in SAMs and l-cysteine in solution. The reaction process was monitored by XPS and electrochemical surface-enhanced Raman spectroscopy (EC-SERS). The surface reaction proceeds as a two-step reaction to give a benzothiazine product, which is in contrast to the much more complicated multiple step reactions in solution. This result suggests that the tight molecular packing in the SAMs does not hinder the intramolecular heterocylization reaction, but prevents the intermolecular coupling reaction from happening. This work provides insights to the control and detection of biomolecule related multistep reactions occurring at solid-liquid interface.

New molecular probe for the selective detection of zinc ion.

A new multisignaling molecular probe DFDB was designed for the selective detection of Zn(2+). DFDB can be synthesized by a simple one-step reaction in high yield. Theoretical calculation suggests a novel sandwich structure of the DFDB·Zn(2+) complex.

Flavanthrene derivatives as photostable and efficient singlet exciton fission materials.

Singlet exciton fission (SF) is believed to have the potential to break the Shockley-Queisser limit for third-generation solar cell devices, so it has attracted great attention. Conventional linear acene based SF materials generally suffer from low triplet energy and poor photostability. We report herein two flavanthrene derivatives, EH-Fla and TIPS-Fla, as new photostable singlet exciton fission materials. These N-doped two-dimensional angular fused acenes have three sets of aromatic Clar sextets, making them significantly more stable than linear acenes with only one sextet. Time-resolved spectroscopy characterization reveals that the SF process occurs in the polycrystalline films of EH-Fla and TIPS-Fla, with maximal triplet yields of 32% and 159%, respectively. The SF processes of these two molecules are mediated by excimer states. In EH-Fla, the low-lying excimer prevents the SF process from occurring effectively, resulting in a low triplet yield. In contrast, the excimer state in TIPS-Fla is mixed with strong CT coupling, which prompts efficient SF and results in a high triplet yield. Our results show that flavanthrene is a promising SF chromophore for photoenergy conversion applications, while a fine-tune of the intermolecular interaction is crucial for achieving high SF efficiency.

2-(Naphthalen-2-yl)azulene.

In the title compound, C(20)H(14), a naphthalene ring system is linked at the 2-position to the 2-C atom of the five-membered ring of an azulene unit. The compound crystallizes with two reasonably similar mol-ecules in the asymmetric unit. Neither mol-ecule is perfectly planar: the r.m.s. deviations from the best fit planes through all non-H atoms are 0.092 and 0.091 Šfor the two mol-ecules. The dihedral angle between the mol-ecular planes is 49.60 (4)°. The naphthalene and azulene ring systems are inclined at dihedral angles of 6.54 (12) and 5.68 (12)° in the two mol-ecules. The crystal structure exhibits two sets of parallel layers, a typical edge-to-face herringbone packing arrangement. The structure is stabilized by an extensive series of weak C-H⋯π inter-actions.

Bioinspired Dual-Responsive Nanofluidic Diodes by Poly-l-lysine Modification.

A smart nanofluidic device attracts attention as it enables to control the physicochemical properties and transportation phenomena, by using stimuli-responsive materials. This work reports a bioinspired modification of a conical ion track-etched polyethylene terephthalate nanopore surface by coating a layer of poly-l-lysine (PLL), which is a commonly used coating in biotechnology to achieve a dual-responsive nanofluidic channel by pH or temperature. The rectification of ionic transportation can be reversed by assembling PLL because of the change of surface bonds from the carboxyl to amine group. The PLL-modified nanopore becomes nonconductive as an "OFF" state at pH 11.5 and at a temperature of 70 °C in solution. The ionic transport in nanopores can be switched to the "ON" (conductive) state, by either decreasing pH or temperature. The transitions between "ON" and "OFF" states present excellent reversibility, which make the PLL-modified nanopores a promising smart nanofluidic device that can be used for drug delivery or biomimic ion/mass transport in future, besides the good biocompatibility and ease of use of PLL modification.